1. Field of the Invention
The present invention relates to a method of and an apparatus for recording information on a recordable optical disc, and more particularly to a method of and an apparatus for measuring and determining an optimum recording power before information is recorded on a recordable optical disc.
2. Description of the Prior Art
There are known compact discs (CD) having diameters of 12 cm and 8 cm. As shown in FIG. 8 of the accompanying drawings, a compact disc has a lead-in area, a program area, and a lead-out area that are arranged successively from an innermost circular boundary on the disc. The compact disc stores a digital signal in the form of an EFM (Eight to Fourteen Modulation) signal. The recorded digital signal includes a main code representing main information such as music information and a subcode such as a time code (Q data) representing time information.
The lead-in area stores index information called TOC (Table of Contents) information. The TOC information contains a subcode indicating the total number of music pieces recorded in the program area, the total playback time of recorded music pieces, and other information. The program area contains a main code representative of music information, Q data of the subcode, track numbers (TNO) indicating the numbers of music pieces, playback times (P-TIME) from the start of the tracks, a total playback time (A-TIME) measured from the track number 1, and other information. The lead-out area contains a lead-out code representing the lead-out area.
The CDs with such a recording format are a medium used for playback only. There has recently been developed a recordable compact disc (R-CD) which has substantially the same format as the conventional CD and which allows additional information to be recorded subsequently. The recording format of the R-CD is referred to as "Orange Book". While the recording format of the R-CD is similar to that of the ordinary CD, it additionally has a PCA (Power Calibration Area) and a PMA (Program Memory Area) that are positioned radially inwardly of the lead-in area, as shown in FIG. 9 of the accompanying drawings.
On tracks of the R-CD, guide grooves are formed being wobbled by the frequency of a carrier of 22.05 KHz which is frequency-modulated by data indicating absolute time information (ATIP: Absolute Time In Pregroove). A laser beam for recording desired information on the R-CD is controlled to follow the guide grooves under tracking control, and the rotational speed of a spindle motor which rotates the R-CD is controlled so that the wobbling guide groove pattern has a central frequency of 22.05 KHz. In this manner, tracking servo and spindle-motor servo processes can be effected on unrecorded R-CDs as well as recorded R-CDs.
The ATIP information will be described below. As shown in FIG. 10 of the accompanying drawings, the ATIP information contains a plurality of frames each composed of 42 bits. The 42 bits of each frame include 4 bits indicative of a sync pattern (SYNC), 8 bits indicative of a minute (MIN), 8 bits indicative of a second (SEC), 8 bits indicative of a frame (FRAME), and 14 bits indicative of an error correcting code (ECC).
The absolute time information represented by the ATIP information equals 1 second in 75 frames as is the case with the Q data of the subcode. In the lead-in area, the absolute time information monotonously increases such that it indicates 99 minutes 59 seconds 74 frames (represented as "99:59:74") at the end of the lead-in area. The absolute time information indicates 00:00:00 at the beginning of the program area, and monotonously increases in the program area.
The manner in which the ATIP information varies across the R-CD is schematically shown in FIG. 12 of the accompanying drawings. The ATIP information in those areas which are radially inward of the program area is indicated by dotted lines, showing that it monotonously increases and indicates 99:59:74 at the end of the lead-in area, as described above. In FIG. 12, the program area has a start frame t.sub.4, the lead-in area has a start frame t.sub.3, the PMA has a start frame t.sub.2, and the PCA has a start frame t.sub.1. These
t.sub.1 =t.sub.3 -00:35:65 PA1 t.sub.2 =t.sub.3 -00:13:25 PA1 t.sub.4 =00:00:00.
In addition to the ordinary absolution time information, the ATIP information includes special information encoded by the combination of the most significant bits (MSB) of the 8-bit data which indicate MIN, SEC, and FRAME (in FIG. 10, the combination of the 5th, 13th, and 21th bits as counted from the beginning of the frame). If the combination of the 5th, 13th, and 21th bits is "101", then the information represented by the 6th, 7th, and 8th bits indicates a recommended recording power, i.e., a recording laser beam intensity, for use with the disc. As shown in FIG. 11 of the accompanying drawings, there are eight recommended recording powers indicated by eight combinations of the 6th, 7th, and 8th bits, ranging from "000" to "111". The recommended recording powers are determined under the conditions that the recording laser beam has a wavelength .gamma. of 780 nm and is generated at a temperature T of 25.degree. C. Since the wavelength .gamma. is temperature-dependent and different objective lenses have different aperture ratios NA, an optimum recording power may not necessarily be the same as any of the recommended recording powers.
The PCA will now be described below. The PCA is an area where test recording is carried out prior to an information recording process, so that the power of the recording laser beam will be optimized for recording desired information in the information recording process. As shown in FIG. 13 of the accompanying drawings, the PCA is composed of a count area CA and a test area TA.
The count area CA has a start frame indicated by (t.sub.3 --00:15:05) and an end frame indicated by (t.sub.3 --00:13:25). The count area CA is divided into 100 areas each having one frame, and these divided areas are numbered C.sub.100 .about.C.sub.1 successively radially outwardly. The area C.sub.1 has an end frame indicated by (t.sub.3 --00:13:55). The area C.sub.1 is followed by 30 reserved frames in the count area CA.
The test area TA has a start frame indicated by (t.sub.3 --00:35:65) and an end frame indicated by (t.sub.3 --00:15:05). The test area TA has innermost 30 reversed frames which are followed by 100 divided areas each having 15 frames, and these divided areas are numbered T.sub.100 .about.T.sub.1 successively radially outwardly. The area T.sub.1 has an end frame indicated by (t.sub.3 --00:15:35). The area T.sub.1 is followed by 30 reserved frames in the test area TA.
The areas C.sub.100 .about.C.sub.1 of the count area CA of the above format correspond respectively to the areas T.sub.100 .about.T.sub.1 of the test area TA, and suitable EFM signals are to be recorded in the areas C.sub.100 .about.C.sub.1. Test recording for measuring an optimum recording laser beam power is carried out in the areas T.sub.100 .about.T.sub.1 of the test area TA. This is because the recommended recording powers indicated by the ATIP information may not necessarily be indicative of an optimum recording power. One of the areas T.sub.100 .about.T.sub.1 of the test area TA is consumed by a single test recording cycle. An actual process for measuring an optimum recording laser beam power will be described later on.
Any area T.sub.n of the test area TA which has once been used by test recording is not available for a next test recording cycle. It is therefore necessary to search for an unused area T.sub.n+1 positioned radially inwardly of the used area T.sub.n for use in the next test recording cycle. The count area CA is provided to facilitate the searching process. More specifically, as shown in FIG. 13, it is assumed that the areas T.sub.1, T.sub.2, T.sub.3 of the test area TA have already been used by test recording. To indicate that the areas T.sub.1, T.sub.2, T.sub.3 have been used, suitable EFM signals are recorded in the corresponding areas C.sub.1, C.sub.2, C.sub.3 of the count area CA, as shown hatched in FIG. 13. No EFM signal is recorded in the area C.sub.4 next to the most recently used area C.sub.3. The unrecorded area C.sub.4 indicates that the corresponding area T.sub.4 of the test area TA is available for test recording. Consequently, the area T.sub.4 may be searched for and test recording carried out therein for measuring an optimum recording laser beam power. After an optimum recording laser beam power has been measured in the area T.sub.4, the area C.sub.4 of the count area CA is searched for, and suitable EFM signal is recorded in the area C.sub.4, indicating that test recording has already been conducted in the corresponding area T.sub.4.
The PMA is an area for storing a recording history of items of information successively recorded in the program area. Specifically, the start addresses and end addresses of track numbers recorded in the program area, for example, are recorded in the PMA in the same format as the TOC information in the lead-in area.
The recording history of successively recorded items of information is stored in the PMA for the following reasons: On a partially recorded disc, information may further be recorded in the remaining blank of the program area. Therefore, the TOC information cannot be recorded in the lead-in area until the completion of recording of all the desired information is finally instructed. Consequently, information about the tracks that have already been recorded is temporarily stored in the PMA. When the user or controller of the disc instructs that no more information will be recorded, the TOC information and a lead-out signal are recorded on the disc. The finalized disc (R-CD), on which the recording of all the necessary information is completed, is then based on the CD format, and can be played back by a disc player for playback only.
After the disc is loaded into a recording apparatus, test recording in the PCA is carried out at least once prior to additional recording of any desired information in the program area. However, if test recording is effected in the PCA at the same time that the disc is loaded into the recording apparatus, then in case the user subsequently ejects the disc without recording any additional information in the program area, the test area TA is unduly consumed. For example, if the user loads and then ejects the disc 100 times without recording any additional information in the program area, then all the test area TA is used up, and no additional information whatsoever can subsequently be recorded in the program area. To eliminate the above drawback, it may be possible to effect test recording only once in the PCA only when the user instructs the recording of information in the program area after the disc is loaded into the recording apparatus.
In the PCA, the areas T.sub.100 .about.T.sub.1 of the test area TA correspond respectively to the areas C.sub.100 .about.C.sub.1 of the count area CA, as described above. After an optimum recording laser beam power is measured in the area T.sub.n of the test area TA, it is necessary to record count information or an EFM signal in the corresponding area C.sub.n of the count area CA. Because of the necessity of recording such count information in the corresponding area C.sub.n of the count area CA, the recording apparatus cannot immediately record additional information in the program area after the test recording. It has heretofore been desired to shorten the time lag that the recording apparatus suffers before it can record additional information in the program area.